1. Field of the invention
The present invention relates to an amorphous silicon film and its production. More particularly, the present invention relates to an amorphous silicon film with wide optical bandgap and high photoelectric conductivity and a method for production of such a film. Also, the present invention relates to a photo-semiconductor device utilizing such an amorphous silicon film.
2. Description of the Prior art
In general, amorphous silicon films for use in photo semiconductor devices such as, for example, photovoltaic devices are required to have a wide bandgap to use incident light effectively.
To this end, so far, it has been proposed to incorporate additives such as carbon or oxygen into amorphous silicon films. However, incorporation of such an additive causes decrease in characteristics of the film, especially, photo electric conductivity, as disclosed in Journal of Non-Crystalline Solids 97&98 (1987) 1027-1034.
On the other hand, amorphous silicon films with a wide bandgap can be produced by increasing the hydrogen concentration in the amorphous silicon film, without incorporation of additives such as carbon. In this case, it is possible to produce amorphous silicon films containing 30 atomic % of hydrogen if the substrate is maintained at a temperature of 100.degree. C. or less during formation of the film. However, if the substrate temperature is not more than 100.degree. C., the photo electric conductivity of the film decreases considerably, thus making it impossible to produce amorphous silicon films with excellent characteristics.